Circuit arrangements for operating lamps which essentially comprise two stages are widely used. A rectified system voltage is fed to a first stage which makes available a DC voltage for a second stage, this DC voltage being referred to in the literature as the intermediate circuit voltage. One function of the first stage is to draw a system current from the system voltage which is as proportional as possible with respect to the system voltage.
The second stage produces an AC output voltage from the intermediate circuit voltage, and this AC output voltage has a frequency which is substantially higher than the frequency of the system voltage. The AC output voltage is fed to a load circuit at a load circuit input. A lamp can be coupled to the load circuit. The load circuit essentially has the function of matching the AC output voltage to the requirements of the lamp. For example, the output impedance of the second stage or the amplitude of the AC output voltage needs to be matched to the lamp by means of a reactance network and/or a transformer.
For the first stage, a SEPIC-type converter (Single-Ended Primary Inductance Converter) is known, for example, from the specification U.S. Pat. No. 6,690,122 (Weirich). The SEPIC is a converter which contains only a first electronic switch. The SEPIC has the advantage that it can provide an intermediate circuit voltage, whose value can be set to be either above or below the value of the amplitude of the system voltage.
For the second stage, inverters having one or more electronic switches are known. The so-called half-bridge inverter which contains two electronic switches which are connected in series, the AC output voltage being applied to the junction of these two electronic switches, is widely known.
Furthermore, inverters are known for the second stage which contain only one electronic switch, such as flux converters, flyback converters or inverse converters.
The two-stage design of the circuit arrangement means a high degree of complexity as regards the number of electronic switches and the drive apparatuses required for them.